Polyethylene resins and polypropylene resins are widely used as major polymers among polyolefin resins in various industrial fields. Because these resins are exceedingly important industrial materials, the various performances thereof are always required to be further improved.
The catalysts for use in producing such polyolefin resins are limited to heterogeneous-system solid catalysts such as Ziegler-Natta catalysts and Phillips catalysts and homogeneous-system catalysts employing a solvent-soluble metal complex, such as metallocene catalysts.
Under the influence of the rapid advances of metallocene catalysts, complexes different from the metallocene complexes are being developed enthusiastically in recent years, such complexes being called post-metallocene complexes. Among such post-metallocene complexes, complexes of late transition metals are attracting attention, and a large number of late transition metal complexes mainly having a bidentate ligand have been reported.
Representative late transition metal complexes having a bidentate ligand include the diimine complex proposed by Brookhart et al. (non-patent document 1) and the salicylaldimine complex proposed by Grubbs et al. (non-patent document 2). These discoveries were followed by reports on late transition metal complexes having various bidentate ligands such as an unsymmetric iminopyridine, pyridinecarboxamide, and iminophophine, and on the usefulness thereof as ethylene polymerization catalysts. Of these complexes, the late transition metal complexes of the iminophosphine type are complexes on which many investigations have been made from both the industrial and the scientific standpoints because these complexes have a nitrogen atom and a phosphorus atom which differ in donor characteristics.
However, in patent documents (patent documents 1, 2, 3, and 4) and non-patent documents (non-patent documents 3 and 4) which relate to late metal complexes having an iminophosphine bidentate ligand, there are the only examples of polymerization for ethylene oligomers or polymers. No report is given therein on polymerization of an α-olefin other than ethylene.